Thin film line sensor for measuring magnetic fields, pressure, vibration or physical displacement

ABSTRACT

A line sensor which utilizes a ferromagnetic coated conductor in combination with another conductor in a line transducer. The line sensor is responsive to stress and to the ambient magnetic field. The impedance of the line transducer varies in accordance with the stress thereon and also in accordance with changes in the ambient magnetic field. A driving signal is introduced into the line transducer and a monitoring circuit detects the variations in the impedance of the line transducer. This enables the line sensor to indicate either individually or in combination disturbances in the ambient magnetic field, seismic movement, and differential displacement of the line transducer due to pressure upon the medium containing the line transducer.

United States Patent Johnson et al.

[451 Nov. 21, 1972 [54] THIN FILM LINE SENSOR FOR MEASURING MAGNETICFIELDS, PRESSURE, VIBRATION OR PHYSICAL DISPLACEMENT 3,490,034 l/1970Marshall, Jr. ..324/43 R Primary Examiner-Robert J. CorcoranAttorney-Charles J. Ungemach and Albin Medved [57] ABSTRACT A linesensor which utilizes a ferromagnetic coated conductor in combinationwith another conductor in a line transducer. The line sensor isresponsive to stress and to the ambient magnetic field. The impedance ofthe line transducer varies in accordance with the stress thereon andalso in accordance with changes in the ambient magnetic field. A drivingsignal is introduced into the line transducer and a monitoring circuitdetects the variations in the impedance of the line transducer. Thisenables the line sensor to indicate either individually or incombination disturbances in the ambient magnetic field, seismicmovement, and differential displacement of the line transducer due topressure upon the medium containing the line transducer.

10 Claims, 6 Drawing Figures [72] Inventors: Gary N. Johnson, RapidCity, S. Dak.; Larry E. Wilson, Excelsior, Minn.

[73] Assignee: Honeywell Inc., Minneapolis, Minn.

[22] Filed: I May 14,1971

[2]] Appl. No.: 143,548

[52] US. Cl. ..324/43 R, 73/517 R [51] Int. Cl. ..G01r 33/02 [58] Fieldof Search ..324/43 R, 47; 73/517 R [56] References Cited UNITED STATESPATENTS 2,643,367 6/1953 Cruzan ..73/517 R 2,841,386 7/1958 Everett..73/517 R 3,239,754 3/1966 Odom,Jr. et al. ..324/47 OSCILLATORDEMODULATOR' AMP.

FILTER ALA M PAIENTEDIBVZI m2 SHEET 1 OF 2 FIG. 2

OSCILLATOR DEMODULATOR INVENTORS GARY N. JOHNSON LARRY .WILSON BYATTORNEY PAIENTEMMZI m2 3.703.681

SHEEI 2 0F 2 FIG. 6

FIG. 5

INVENTORS GARY N. JOHNSON LARRY WILSON ATTORNEY BACKGROUND OF THEINVENTION The present invention isan improvement in magnetic, pressure,and seismic linesensors.

The ease of deployment and continuous sensitivity of the linesensor makeit useful in security applications and in research and exploration.Commonly known pressure and seismic .line sensors employ fluid filledlines, resistance-type lines, capacitive-type lines, or lines containinga combination of permanent magnets and coils. The present line sensor isconstructed in the manner of a coaxial transmission line, therebyeliminating the use of fluids, coils, and separated conducting plates.This allows the present line sensor to be constructed and deployed withless difficulty than is experienced with existing line sensors. Also,due tothe simplified construction, the present line sensor has increasedreliability.

Furthermore, commonly known line sensors are not responsive to inputs ofmore than one typeas is possible with the present line sensor which maybe constructed to be responsive to magnetic fluctuations,

seismic disturbances, or pressure inputs. Such multiple sensitivitymakes the present line sensor valuable in security applications where itis desired to monitor the movement of ferromagnetic masses as well asthe presence of pressure or vibration.

BRIEF SUMMARY OF THE INVENTION The present invention employs aferromagnetic coated conductor in a line transducer for sensing magneticand environmental disturbances either individually or in combination. Awirelike conductor has a ferromagnetic coating thereon which hasa netmagnetization vectorabout the conductor for sensing magneticdisturbances and which is magnetostrictive for sensing physicalenvironmental disturbances. A second conductor encloses thecoatedconductor for its entire length and an insulating material separates thetwo conductors. v

The two conductorsare connected to a monitoring circuitand also to anoscillator which causes the magnetization vector to oscillate about itspredisposed orientation. A variation in the ambient magnetic fieldcauses further disorientation of the vector which causes the inductiveimpedance of the coated conductor to vary accordingly. This variation inimpedance is detected by the monitoring circuit.

The magnetostrictive character of the ferromagnetic coating results in asimilar variation in the inductive impedance in accordance with thestrain imposed upon the coated conductor. This feature allows the linesensor to be responsive to. strain within the line transducer caused byeither static or dynamic pressure or physical movement.

The objective of the present invention is to provide an improved linesensor that is responsive to the ambient magnetic field.

Another objective isto provide an improved line sensor that isresponsive to displacement of the line transducer.

A further objective is to provide an improved line sensor that isresponsive to seismic movement.

Still another objective is to provide a line sensor that is responsiveto a combination of the above inputs.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross section view of oneembodiment of the line transducer in the line sensor;

FIG. 2 is a cross section view of the line transducer of FIG. 1 takenalong the line 2-2 of FIG. 1;

FIG. 3 is a cross section view of a second embodiment of the linetransducer in the line sensor;

I FIG. 4 shows a preferred embodiment of the line sen- I sor accordingto the present invention;

FIG. 5 is a cross section view of a third embodiment of the linetransducer; and

FIG. 6 is a cross section view of a fourth embodiment of the linetransducer.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2 aline transducer 10 of the line sensor contains a beryllium copperconductor 11 which has a ferromagnetic coating 12 applied thereon.

Ferromagnetic coating 12 is a nickel-iron alloy which is approximately20 percent iron and percent nickel.

Ferromagnetic coating 12 has a net magnetization vec- I tor whichresults from the application of a constant magnetic field aboutconductor 11 during the plating of ferromagnetic coating 12 thereon. Asecond conductor 14 encloses conductor 11 and is separated therefrom byan insulating material 13. A protective covering 15 FIG. 3 shows a linetransducer 16 which is identical to line transducer 10 except thatconductor 11 is separated from second conductor 14 by a plurality ofequally spaced circular nonconducting spacers 17. A plurality of smallmasses 18 are attached to conductor 1 1 equidistant between successivespacers 17 FIG. 5 shows a line transducer 26 that is identical to linetransducer 10 except that the cavity within insulating material 13 has agreater diameter than conductor 11 with its ferromagnetic coating 12.Therefore, conductor 11 is not tightly bound and has intervals ofnoncontact with insulating material 13.

FIG. 4 shows a preferred embodiment of the line sensor whereinconductors 11 and 14 of line transducer l0, 16, 25, or 26 are connectedto the output of an oscillator 19. Conductors 11 and 14 are furtherconnected to a demodulator 20 which is connected to an amplifier 21.Amplifier21 is connected to a passband filter 22 which is connected toan alarm 23.

OPERATION Line transducer 10 is responsive to the ambient magnetic fieldbecause of the magnetization of ferromagnetic coating 12. Linetransducer 10 becomes operative when connected to the circuitry shown inFIG. 4. Oscillator 19 drives conductors 11 and 14 with an oscillatingsignal having a constant frequency and current amplitude which causesthe magnetization vector of ferromagnetic coating 12 to oscillate fromits predisposed position because of the alternating electromagneticfield created about conductor 11 by the oscillating signal. Variationsin the ambient magnetic field will further disorient the magnetizationvector in accordance with the variation in the ambient magnetic field.The resulting variation in the orientation of the magnetization vectorcauses a corresponding change in the inductive impedance of conductor11. This change in the inductive impedance causes a corresponding changein the impedance of transducer 10. The varying impedance of transducerresults in amplitude modulation of the oscillating signal generated byoscillator 19. Demodulator is employed to detect the amplitudemodulation of the oscillating signal and to produce an output signalrepresentative of that modulation. In a security application for whichthe preferred embodiment was designed, the output of demodulator 20 isintroduced into a system such as is described by amplifier 21, passbandfilter 22, and alarm 23. Alarm 23 is any desired apparatus capable ofindicating that an output signal from demodulator 20 is characteristicof an intruders amplitude and frequency signature.

Line transducer 10 may also be responsive to pressure by makingferromagnetic coating 12 magnetostrictive which is achieved by slightlyvarying the percentage of iron and nickel in ferromagnetic coating 12from 20 percent iron and 80 percent nickel. Pressure upon linetransducer 10 causes displacement of conductor 11. Because of themagnetostrictive property of ferromagnetic coating 12, such displacementcauses a disorientation of the magnetization vector. The inductiveimpedance of conductor 11 varies accordingly, thereby varying theimpedance of line transducer 10 in correspondence with the pressurethereon. This variation in impedance is detected in the same manner asdescribed above. The sensitivity of line transducer 10 to the ambientmagnetic field can be eliminated by making conductor 14 ferromagneticwhich shields conductor 1 1. Therefore, line transducer 10 would besensitive only to displacement due to direct pressure thereon orindirect pressure upon the medium supporting line transducer 10.

An alternate embodiment of line transducer 10 is also depicted in FIG.5. Conductor 11 with its ferromagnetic coating is not bound toinsulating material 13 and does not respond either to direct pressure orto forces which tend to longitudinally stress line transducer 10.Conductor 11 will be subject only to bending forces imposed upon linetransducer 10. As such, the strain imposed on conductor 11 will bedetermined by the radius of the bend or differential displacement ofline transducer 10. In this embodiment, line transducer 10 will beresponsive only to localized forces and unresponsive to uniform forcesacting along the length of the transducer.

Conductor 14 acts as a shield for the electromagnetic field generatedabout conductor 11, thereby preventing the detection of the linetransducer due to stray electromagnetic radiation. This shielding effecthas particular value in security applications.

FIG. 6 shows a line transducer which is an alternate embodiment of linetransducer 10. Conductor 14 does not enclose conductor 11 in linetransducer 25 but instead lies substantially parallel to conductor 11.The operation of line transducers l0 and 25 is identical. However, theshielding of conductor 1 l by conductor 14 as described above is notpresent in line transducer 25.

Referring to FIGS. 3 and 5, line transducers 16 and 26 are primarilyresponsive to seismic movement although also responsive to pressure andto the ambient magnetic field if so desired. Line transducer 26 isidentical to line transducer 10 except that conductor 11 is not tightlycontained within insulating material 13, and ferromagnetic coating 12 ismagnetostrictive. The inner diameter of insulating material 13 isgreater than the diameter of conductor 11, thereby allowing conductor 11freedom of movement within line transducer 26. Conductor 11 in linetransducer 26 is a very small diameter wire which has a tendency tocoil. Therefore, as shown in FIG. 5, conductor 11 comes into contactwith insulating material 13 only at various points along the length ofline transducer 26, thereby leaving intervals of noncontact. Seismicmovement causes a strain in conductor 11 due to the bending stresscaused by the movement of the distributed weight of conductor 11 alongthe intervals of noncontact with insulating material 13. This makes linetransducer 26 sensitive to seismic movement. The displacement of linetransducer 26 is sensed in the same manner as described for linetransducer 10.

Line transducer 16 shown in FIG. 3 is similar to line transducer 26except that insulating material 13 is replaced by a plurality ofcircular spacers 17 to prevent contact between conductors 11 and 14 andto allow conductor 11 some degree of movement. When line transducer 16is subjected to an acceleration or vibration, masses 18 cause conductor11 to be stretched between spacers 17. The resulting strain of conductor11 is detected in the same manner as described in the operation of linetransducer 10. As stated before, the sensitivity of line transducers 16and 26 to magnetic disturbances can be eliminated by making conductor 14ferromagnetic.

The variations in inductive impedance of conductor 11 could be detectedthrough frequency modulation as opposed to amplitude modulation bymaking the line transducer part of the frequency determining circuitryof oscillator 19.

Although line transducers 10, 16, 25, and 26 function properly as openended transmission lines, improved results may be obtained by connectingconductors 11 and 14 of the line transducers at one end thereby makingeach of the above line transducers function as close-ended transmissionlines. Whether an open or close-ended transmission line is desired foroptimum performance depends upon the oscillating signal frequency andthe length of the line transducer.

As has been described, the line sensor can be sensitive to magnetic,pressure and seismic disturbances, to differential displacement, to anycombination of the influences, or all simultaneously if so desired. Theline transducer of the line sensor can either be buried within somemedium such as the earth or attached to the surface of that medium forsensing magnetic disturbances in the ambient magnetic field or forsensing pressure upon or seismic movement of that medium. Thedescription contained within this specification is preferred and is notintended to limit the scope and intent of the present invention.

I claim as my invention:

1. A line sensor for indicating at least one of a disturbance in theambient magnetic field, a pressure 5 exerted thereon, a vibrationimposed thereon, and physical displacement of a portion thereofcomprising:

representative signal of said modulation;

an amplifier connected to said demodulator to receive saidrepresentative signal;

a filter network connected to said amplifier for passing only said,representative signals within a desired frequency band; and

an alarm connected to said filter network, said alarm a secondconductorwhich in combination with said first conductor forms a transmission linehaving a characteristic impedance;

an oscillator for producing an output signal at a pair of outputterminals;

means connecting said output terminals to said first and secondconductors; and

monitoring means connected to said first and second conductors forsensing distortion of said output signal due to fluctuations in theimpedance of said first and second conductors that are caused bydisturbances in the orientation of said magnetization vector in responseto strain imposed upon said first conductor because of at least one ofpressure, vibration, and displacement imposed thereon and a disturbancein the ambient magnetic field.

2. The line sensor of claim 1 wherein said second conductor encloses thelength of said first conductor.

3. The line sensor of claim 2 wherein said second conductor is aferromagnetic material.

4. The line sensor of claim 3 wherein said monitoring means comprises:

a demodulator connected to said first and second conductors fordetecting amplitude modulation of said output signal due to saidfluctuations in said impedance, said demodulator producing a beingresponsive to said representative signals passed by said filter network.

5. The line sensor of claim 4 and a protective covering enclosing saidsecond conductor.

6. The line sensor of claim 2 wherein said insulating means supportssaid first conductor with its ferromagnetic coating at a plurality ofpredetermined points along the length of said first conductor therebyleaving predetermined intervals of noncontact between said predeterminedpoints such that said first conductor with its ferromagnetic coating isfree to move within said intervals independent of said insulating means.

7. The line sensor of claim 6 and a plurality of masses attached to theferromagnetic coating of said first conductor, wherein one of saidplurality of masses is attached at each said interval between saidpoints of contact with said insulating means.

8. The line sensor of claim 7 wherein said second conductor is aferromagnetic material.

9. The line sensor of claim 8 wherein said monitoring means comprises:

a demodulator connected to said first and second conductors fordetecting amplitude modulation of said output signal due to saidfluctuations in said impedance, said demodulator producing arepresentative signal of said modulation;

an amplifier connected to said demodulator to receive saidrepresentative signal;

a filter network connected to said amplifier for passing only saidrepresentative signals within a desired frequency band; and

an alarm connected to said filter network, said alarm being responsiveto said representative signals passed by said filter network.

10. The line sensor of claim 9 and a protective covering enclosing saidsecond conductor.

1. A line sensor for indicating at least one of a disturbance in theambient magnetic field, a pressure exerted thereon, a vibration imposedthereon, and physical displacement of a portion thereof comprising: awire-like first conductor having a ferromagnetic coating thereon, saidcoating have a predisposed net magnetization vector and further beingmagnetostrictive; an insulating means enclosing said coated firstconductor, said insulating means having internal dimensionssubstantially exceeding the dimensions of said coated first conductor,such that said coated first conductor is free to move with respect tosaid insulating means; a second conductor which in combination with saidfirst conductor forms a transmission line having a characteristicimpedance; an oscillator for producing an output signal at a pair ofoutput terminals; means connecting said output terminals to said firstand second conductors; and monitoring means connected to said first andsecond conductors for sensing distortion of said output signal due tofluctuations in the impedance of said first and second conductors thatare caused by disturbances in the orientation of said magnetizationvector in response to strain imposed upon said first conductor becauseof at least one of pressure, vibration, and displacement imposed thereonand a disturbance in the ambient magnetic field.
 1. A line sensor forindicating at least one of a disturbance in the ambient magnetic field,a pressure exerted thereon, a vibration imposed thereon, and physicaldisplacement of a portion thereof comprising: a wire-like firstconductor having a ferromagnetic coating thereon, said coating have apredisposed net magnetization vector and further being magnetostrictive;an insulating means enclosing said coated first conductor, saidinsulating means having internal dimensions substantially exceeding thedimensions of said coated first conductor, such that said coated firstconductor is free to move with respect to said insulating means; asecond conductor which in combination with said first conductor forms atransmission line having a characteristic impedance; an oscillator forproducing an output signal at a pair of output terminals; meansconnecting said output terminals to said first and second conductors;and monitoring means connected to said first and second conductors forsensing distortion of said output signal due to fluctuations in theimpedance of said first and second conductors that are caused bydisturbances in the orientation of said magnetization vector in responseto strain imposed upon said first conductor because of at least one ofpressure, vibration, and displacement imposed thereon and a disturbancein the ambient magnetic field.
 2. The line sensor of claim 1 whereinsaid second conductor encloses the length of said first conductor. 3.The line sensor of claim 2 wherein said second conductor is aferromagnetic material.
 4. The line sensor of claim 3 wherein saidmonitoring means comprises: a demodulator connected to said first andsecond conductors for detecting amplitude mOdulation of said outputsignal due to said fluctuations in said impedance, said demodulatorproducing a representative signal of said modulation; an amplifierconnected to said demodulator to receive said representative signal; afilter network connected to said amplifier for passing only saidrepresentative signals within a desired frequency band; and an alarmconnected to said filter network, said alarm being responsive to saidrepresentative signals passed by said filter network.
 5. The line sensorof claim 4 and a protective covering enclosing said second conductor. 6.The line sensor of claim 2 wherein said insulating means supports saidfirst conductor with its ferromagnetic coating at a plurality ofpredetermined points along the length of said first conductor therebyleaving predetermined intervals of noncontact between said predeterminedpoints such that said first conductor with its ferromagnetic coating isfree to move within said intervals independent of said insulating means.7. The line sensor of claim 6 and a plurality of masses attached to theferromagnetic coating of said first conductor, wherein one of saidplurality of masses is attached at each said interval between saidpoints of contact with said insulating means.
 8. The line sensor ofclaim 7 wherein said second conductor is a ferromagnetic material. 9.The line sensor of claim 8 wherein said monitoring means comprises: ademodulator connected to said first and second conductors for detectingamplitude modulation of said output signal due to said fluctuations insaid impedance, said demodulator producing a representative signal ofsaid modulation; an amplifier connected to said demodulator to receivesaid representative signal; a filter network connected to said amplifierfor passing only said representative signals within a desired frequencyband; and an alarm connected to said filter network, said alarm beingresponsive to said representative signals passed by said filter network.